1) Field of the Invention
The present invention deals with a screwing head for screwing the ring nut of a small trigger-type pump, commonly called trigger, on a vessel.
2) Description of Related Art
As known, a trigger is equipped with a float composed of a small pipe aimed to be inserted into the vessel, further comprising an externally toothed ring nut which is free of rotating with respect to the trigger body and is internally threaded to be associated with the corresponding threading obtained on the vessel neck to be plugged.
The screwing head is used in connection with a carousel-type (rotating) or a linear-type machine and, next to every machine workstation, a washer is provided which supports the vessel to be screwed, while the screwing head comprises clamping means of the trigger ring nut which screw it onto said vessel.
The head is actuated by a cam which handles a slide which lowers the clamping means, generally composed of a pair of rollers which are kinematically connected through two arms with the motoring device of the screwing head so that, once arranged in contact with the ring nut, they screw it onto the vessel.
Following the tightening, to avoid that the torque impressed onto the head exerts an action which is greater than the threading sealing limit, a permanent magnet-type clutch takes care of detaching the rotation action to the rollers.
A prior art inconvenience which uses only two tightening rollers, is that, to avoid sliding between these latter ones and the knurled ring nut, a certain energic action must be created, namely a certain pressure onto the ring nut, creating distortions and abrasions thereon.
A prior art proposed solution to solve the above inconvenience has been doubling the number of rollers acting on the ring nut in order to reduce the local contact pressure, though keeping unchanged the number of oscillating arms for approaching the ring nut; this solution modifies the operating angle of each roller onto the ring nut (not radial any more) at the same time creating slidings between components and unpleasant abrasions to the knurled part of the ring nut.